1. Field of the Invention
The present invention relates to a light emitting module and an optical wavelength converting member.
2. Related Art
Recently, as light sources for illuminating high intensity light such as lamp units for illuminating light toward front areas of vehicles in order to achieve purposes of long lifetime and reductions of power consumption, light emitting modules having light emitting elements such as LEDs (Light Emitting Diodes) have been developed. In order to employ the light emitting modules in such a field, not only emissions of white light by the light emitting modules must be realized, but also high luminance and high luminous flux are required for the light emitting modules. For instance, in order to improve deriving efficiencies of white light, illuminating apparatuses equipped with light emitting elements for mainly emitting blue light, yellow color-series fluorescent members, and blue color-transmitting yellow color-series reflecting means have been developed (refer to, for example, JP-A-2007-059864). In the illuminating apparatuses, the yellow color-series fluorescent members mainly emit yellow light by being excited by the blue light, and the blue color-transmitting yellow color-series reflecting means pass therethrough the blue light emitted from the light emitting elements and reflect thereon light having wavelengths longer than, or equal to those of the yellow light emitted from the yellow-series fluorescent members. Also, for instance, in order to increase converting efficiencies, structural members equipped with ceramic layers disposed within paths of light irradiated by light emitting layers have been proposed (refer to, for example, JP-A-2006-005367).
Also, when projection portions are spread all over a light output plane, it is known that a predetermined relationship is established among wavelengths of light, heights of the projection portions, and reflectance factors (refer to, for instance, non-patent document 1).
<Non-Patent Document 1>
“High Performance Reflection Preventing Film based upon Sub-wavelength Structure” SWC” written by Takeharu Okuno, OPTICAL TECHNICAL CONTACT, pages 83 to 88, Feb. 20, 2009 issued by Japan Opto-Mechatronics Association
In such a case that the projection portions have been provided on the light transmitting member, the below-mentioned fact can be revealed: That is, if the height “h” of the projection portions becomes larger than approximately ½ of the wavelength of the light, then the reflectance factor “R” becomes substantially zero %, namely, substantially all of light pass through the light transmitting member. Conversely, when the height “h” of the projection portions becomes smaller than approximately ½ of the wavelength of the light, it is revealed that the smaller the height “h” becomes, the larger the reflectance factor “R” becomes.
For example, as explained in the case that a light emitting module is employed in the above-described lamp unit, in such a case where it is required to realize high illuminance and high luminous intensity while a wavelength of light emitted from a light emitting element is converted, there is a large problem that a deriving efficiency of the light from the light emitting element is improved. However, for example, when an incident angle of light to a light output plane of a fluorescent member becomes larger than a total reflection critical angle, the light is not outputted, but is reflected within the fluorescent member, which may cause a deriving efficiency of the light to be lowered. On the other hand, as to improvements in such a deriving efficiency of light, as explained in the above-described non-patent document 1, there are possibilities that higher deriving efficiencies of light can be realized by considering the relationship between the heights of the projection portions and the reflectance factors. For example, in vehicle-purpose lighting devices, light emitting modules having high luminance are required while light output directions thereof are defined to a single direction. Since light other than light along main light output direction constitutes glares with respect to pedestrians and opposite-direction driving cars, it is required to reduce the first-mentioned light in minimum.